Chapter 24: DNA viruses

Lytic cycle

Lytic cycle

• Rapid course of a viral infection

• Adsorption

• Penetration

• Replication

• Maturation

• Release

Chronic infection

• Virus detectable in tissue samples

• Multiplying at a slow rate

• Symptoms are mild or absent

Latent infections

• After a lytic cycle

• Virus enters a dormant phase

• Generally not detectable

• Can reactivate and result in recurrent infections

Oncogenic

Can develop tumors

Teratogenic

• Can cross the placenta, causing developmental distrubances and perament defects

Small pox

• Is a poxvirus that produces eruptive skin pustules (pox) that leave scars

• First disease to be eliminated via vaccination

• Exposure though inhalation or skin contact

• Causes fever, malaise, prostration, and rash

Variola major

• Highly virulent

• Caused toxemia, shock, and ontravascular coagulation

Variola minor

Less virulent

Small pox vaccination

• Uses a single drop of vaccina virus

• Was punctured into the skin with a double pronged needle

Molluscipoxvirus

• More common pox virus

• Causes molluscum contagiosum

Molluscum contagiosum

• Skin disease caused my Molluscipoxvirus

• Occurs in pacific islands ; primary infection of children

• Transmitted by contact and fomites

• Is an STD in the US

• Lesions are small, smooth macules in genetal area and thighs

• AIDS patients suffer an atypical form what attacks the skin of the face and forms tumor like growths

Poxviruses treatment

• Freezing

• Electric cautery

• Chemical agents

Herpesviruses

• All members show latency and cause recurrent infection

• Viral DNA forms episome

• Clinical complications of latency and recurrent infections become more severe with conditions compomising the immune defense

• Common and serious opportunists among AIDS patients

Herpesvirus family

• Herpes simplex 1

• Herpes simplex 2

• Varicella zoster virus

  • Chicken pox

  • Shingles

• Epstein barr virus

• Cytomegalovirus

• Human herpesvirus 6

• Human herpesvirus 7

• Herpesvirus 8

HSV-1

• Fever, blisters, and genital infections

• Usually lesions on the oropharynx, cold sores, and fever blisters

• Occurs in early childhood

HSV-2

• Fever, blisters, and genital infections

• Legions on the genitalia, possibly oral

• Occurs in ages 14-29

• Can be spread with out visible lesions

Herpes simplex transmision

• By direct exposure to secretions containing the virus

• Multiplies in sensory neurons

  • HSV-1 enters the 5th cranial nerve

  • HSV-2 enters the lumbosacral spinal nerve trunk ganglia

Herpes labialis (HSV-1)

• Fever blisters or cold sores

• Most common recurrent HSV-1 infection

Herpetic gingiovastomatitis (HSV-1)

• Especially in young children

• Inflammation of the oral mucosa

  • Gums, toung, soft palate, and lips

Herpetic keratitis (HSV-1)

• Ocular herpes

• Inflammation of the eye; gritty feeling, conjunctivitis, sharp pain, sensitivity to light

• Latent virus travels to the ophthalmic rather than the mandibular branch of the trigeminal nerve

Genital herpes (HSV-2)

• Herpes genitalia

• Starts with malaise, anorexia, fever, and bilateral swelling and tenderness in the groin

• Clusters of sensitive vesticles on the genetalia, perineum, and buttocks

• Urethritis, painful urination, cervicitis, itching

• Recurrent bouts are less severe and are triggered by menstruation, stress, and concurrent bacterial infection

Neonatal herpes (HSV 1&2)

• Potentially fatal in the neonate

• Infant is contaminate by the mother before or during birth

• Infection of the mouth, skin, eyes, and CNS

Herpetic whitlow (HSV 1&2)

• HSV can penetrate a break in the skin and cause a localized infection

• Usually on one finger

• Extremely painfull and itchy

HSV-1 encephalitis

• Rare complication but most common sporadic form of viral encephalitis in the US

• Life threatening

• Immunodeficiency are prone to severe and disseminated herpes

Varicella zoster virus

• Herpesvirus 3

• Infection transmitted by respiratory droplets and contact

• Diagnosis by cutaneous manifestations

• Treated with acyclovir, famciclovir, live attenuated vaccine

Varicella

• Chicken pox

• Herpes virus 3

• Primary infection

• Characteristic vesicles

• Virus enters the neurons and remains latent

Herpes zoster

• Shingles

• Herpesvirus 3

• Reactivation of the virus

• Dermatomes; more common in older adults

Cytomegalovirus

• Herpesvirus 5

• Prodeces giant cells with nuclear and cytoplasmic inclusions

• Transmitted in saliva, respiratory mucus, milk, urine, semen, and cervical secretions

• Latent in various tissues

• Infections are asymptomatic

Epstein barr virus

• Herpesvirus 4

• Ubititous virus; infects lymphoid tissue and salivary glands

• Transmission via direct oral contact and contamination with saliva

• Mononucleosis (mono)

Infectious mononucleosis (EBV)

• Sore throat

• High fever

• Cervical lymphadenopathy

• Develops 30-50 days after incubation

Burkitt lymphoma (EBV)

• B cell malignancy

• Usually develops in the jaw and grossly swells the cheek

• Affects central african children

Nasopharyngeal carcinoma (EBV)

• Malignancy of epithelial cells

• Older chinease and african men

Human herpes virus - 6

• Human b-lymphotropic virus

• Transmission via close contact with saliva and secretions

• Causes roseola

• Adults may get mono-like symptoms, lymphadenopathy, and hepatitis

• Associated with hidgkin’s lymphoma, oral carcinoma, and t-cell leukemias

Roseola (HHV-6)

• Acute febrile disease in babies 2-12mo

• Begins with fever, followed by a faint maculopapular rash

• Kaposi’s sarcoma-associated virus

• HHV-8

• Linked with common tumor of AIDs patients

• Involved in multiple myeloma

Hepatitis

• An inflammatory disease of liver cells that may result from infection by several viruses

• Interferes with the liver’s excretion of bile pigments

• Bilirubin accumulartes in the blood and tissues, causing jaundice

Viruses involved in hepatitis

• DNA viruses (hepadnaviruses)

  • Hepatitis B virus (HBV)

• RNA viruses

  • Hepatitis A virus (HAV)

  • Hepatitis C virus (HCV)

  • Hepatitis E virus (HEV)

  • Hepatitis D virus (HDV)

Hepadnaviruses

• Enveloped DNA viruses

• Never been grown in tissue culture

• Unusual genome containong both double and single stranded DNA

• Tropism for liver

Hepatitis B virus

• Multiplies exclusively in the liver; chronic

• Minute amounts of blood, blood products can transmit infection

• Sexually transmitted

• Increases risk of liver cancer

  • Hepatocellular carcinoma

Adenoviruses

• Nonenvelopes dsDNA

• 30 types associated with human disease

• Infects lymphoid tissues, respiratory, and intespinal epithelia and conjunctiva

• Spreads by respiratory and ocular secretions causes colds, pharyngitis, conjunctivitis, ketatoconjunctivitis, and acute hemorrhagic cystitis

Human papillomavirus

• Causes papilloma to form

• Transmissilbe through direct contact or contaminate fomites

• Most common warts regress over time

• Can be removed chemically and physically

Papilloma

• Squamous epithelial growth, wart, or verruca

Common seed warts

• Painless, elevated, rough growth

• On fingers, etc

Plantar warts

• Deep, painfull

• On soles of feet

Genital warts

• Most common STD in the US

• Morphology ranges from tiny, flat, inconspicuous bumps to extensive, branching, cauliflower-like masses

Human parvovirus

• B19 causes erythema infectiosum

• Rash of childhood

• Children may have fever and rash on cheeks

• Sever fatal anema can result if pregnant women transmits virus to fetus